<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .right {
            color: green;
        }

        .wrong {
            color: red;
        }
    </style>
</head>

<body>
    <input type="text" class="uname"> <span>请输入用户名</span>

    <script>
        var reg = /^[a-zA-Z0-9-_]{9,16}$/;
        var uname = document.querySelector('.uname');
        var span = document.querySelector('span');
        uname.onblur = function () {
            if (reg.test(this.value)) {
                console.log('正确');
                span.className = 'right';
                span.innerHTML = '用户名格式正确';
            } else {
                console.log('错误');
                span.className = 'wrong';
                span.innerHTML = '用户名格式错误';
            }
        }
    </script>
</body>

</html>